Conventionally, there has been an affiliate system as advertisement that uses a network. In the affiliate system, a person introduces a product and the like of a seller by setting a link or the like on a webpage and, when a customer clicks through the link or the like and acquires the product by purchasing it or the like, a predetermined reward is given to the person (for example, PLT1). Especially, since many customers refer an introduction or evaluation made by their acquaintances in determining the purchase, the affiliate system is very useful.